The present invention relates, in general, to elevated tanks and, more particularly, to methods of constructing elevated tanks.
In slipforming, the forms are 3 to 4 feet high, and move upwardly at about one foot per hour either continuously or intermittently continuously. In the latter case, the crew may work on only one shift per day because of economics, or restrictions on noise, or lack of trained people for more than one shift.
In any case, the concrete being exposed at the bottom edge of the form is stiff and of low but sufficient strength to carry the loads applied thereto.
In jumpforming, the same type forms are used, but may be of a greater height and increased strength. The forms are positioned and filled with concrete. The concrete is allowed to set for hours or days until sufficiently strong, and then moved upward and the next portion cast. This process is not of a continuous nature, but intermittent. One jumps the forms upwardly between pours using jacks, or the like, similar to those used in slipforming.
In the present disclosure, terms such as "forming", "formwork", and the like, will be used to include both slipforming and jumpforming. A specific embodiment using slipforming will be presented, but it is to be noted that such embodiment is not intended as a limitation, but is an example only.
Slipforming concrete walls is a well known construction technique. Basically, slipforming comprises positioning a formwork, pouring concrete into the formwork, and then, while the concrete is setting, moving the same formwork upwardly to pour freshly mixed concrete on top of the first concrete. This procedure is repeated until the desired height is attained. The repetition may be continuous from start to finish or intermittently continuous such as may be accomplished during day shifts only. Known slip-forming apparatus uses a self-climbing formwork, and reinforcing steel is placed as the forms move upwardly. This technique has been successfully utilized in construction of buildings, water towers, bridge piers, chimneys, and the like.
Methods of constructing elevated structures are disclosed in U.S. Pat. Nos. 3,201,502, 3,805,369, 4,197,689, 3,092,216, 3,073,018; and U.S. Pat. No. 4,206,162 discloses a method of constructing concrete enclosures using a bottomless form.
All of the known methods of erecting elevated tanks either require the completed tank or the completed parts of the tank to be hoisted onto a completed supporting wall, thereby requiring heavy hoisting equipment, or requiring hoisting jacks to lift the completed tank plus the completed portions of the support wall, thereby again requiring heavy lifting equipment strong enough to support and lift the entire completed assembly.
Also, it is advantageous from a safety and efficiency viewpoint to assemble as much of the structure as close to the ground as possible. In such a case, the structure is fully assembled at or near ground level where access is easier and subsequent concrete placement is done from substantial platforms attached to the slipforms.
Thus, there is need for a method of erecting elevated tanks which does not require the use of extremely heavy hoisting equipment, and which utilizes manpower as close to the ground as is practically feasible.